The present invention relates to a solar canopy system and method for reducing canopy support structure design loadings. More particularly, the present invention relates to a solar canopy system having two or more non-parallel solar panel assemblies having a support structure design based on instantaneous time averaging of the measured wind loadings of the two or more non-parallel solar panels.
One obstacle to cost reduction of solar photovoltaic (PV) canopy structures is the wind loading prescribed by building codes. Currently, the majority of the canopy structure vendors in the industry do not utilize wind tunnel testing as measuring the wind loading on coplanar panel assemblies does not yield a useful decrease in loading compared to code prescribed loads.
The PV canopy structures available openly in the industry have substantially the same general configuration as the monoslope free roof PV canopy shown in FIG. 1 and hereafter referred to as the monoslope PV canopy 1. Generally, the monoslope PV canopy 1 has a vertical post 2 extending above a grade 3 and anchored below the grade 3 by a foundation 4. One or more solar panels 5 are supported on a beam 6 by purlins 7 extending between the panels 5 and the beam 6. The beam 6, in turn, is mounted on the post 2 at an angle θ, such that the total canopy protected (or horizontal) width WH is less than the total canopy panel width WT.
The structure of the monoslope PV canopy 1 may be found in the American Society of Civil Engineers Standard for Minimum Design Loads for Buildings and Other Structures, ASCE/SEI 7-10 (hereafter referred to as ASCE 7-10) in FIGS. 27.4-4 for monoslope free roofs, a portion of which is reproduced in FIGS. 2A and 2B herein. The direction of the wind γ in FIG. 2A is zero degrees; the direction of the wind γ in FIG. 2B is one-hundred eighty degrees. CNW and CNL are the net pressure contributions from the top and bottom surfaces for the windward and leeward half of the roof surfaces, respectively. “L” is the horizontal length of the roof measured in the along wind direction. “h” is the mean roof height. 9, is the angle of the plane of the roof from horizontal. The net instantaneous wind loadings CNW and CNL are determined by wind tunnel testing and are provided in ASCE 7-10, FIGS. 27.4-4 for roof angles from zero to forty-five degrees.
It is well accepted within the solar power industry that the wind pressures prescribed in ASCE 7-10, FIGS. 27.4-4 are representative of the real world loading of these structures. For this reason, the largest suppliers of PV canopy structures do not typically utilize any wind tunnel testing in the design of their products.
The pitched roof PV canopy structure shown in FIG. 3 is one example of a structure with two or more non-parallel planes of solar panel surfaces. Currently, this type of structure is not widely utilized within the industry although examples do exist. There are several downsides to this structure when compared to the structure shown in FIG. 1 including energy production (“yield”), direct current (DC) and alternating current (AC) wiring costs, and structural costs. Furthermore, the wind loading coefficients prescribed for canopy structures with two or more non-parallel planes of solar panels can result in higher wind loading and thus higher costs than the single plane of solar panels design. These coefficients can be seen to be as high for pitched free roofs and troughed free roofs as for monoslope free roofs (See, ASCE 7-10, FIGS. 27.4-5 and FIGS. 27.4-6, not shown herein). As shown diagrammatically in FIG. 3, for non-parallel panel surfaces that are not sufficiently structurally connected to allow net, instantaneous pressure measurements across the total combined area, wind loads F1 and F2 are currently determined separately and the total net wind load F3 is calculated as the sum of the worst-case F1 and F2 load measurements, which occur at different times. In contrast to the total net wind load F3 shown in FIG. 3, the net, instantaneous pressure measurements of the total area of structurally connected, non-parallel panel surfaces results in a lower total force F3′ as shown in FIG. 4 since in this instance, the loads F1′ and F2′ are in opposite directions and occur at the same time.
Accordingly, under current practice, the wind loading coefficients prescribed for canopy structures with two or more non-parallel planes of solar panels (see, FIG. 3) can result in higher wind loading and thus higher costs than the single plane of solar panels designs based on the wind loading coefficients shown in ASCE 7-10, FIGS. 27.4-4. Therefore, there is a need for a design methodology for canopy support structures for two or more non-parallel planes of solar panels based on determining the net instantaneous wind loading across the total combined area of the non-parallel planes of solar panels.